Information Series 022

Information Series 022

The porosities, and the saturations with oil and with water, of Athabasca oil sands are of interest and importance. A considerable volume of data on these properties is becoming available from the reports of oil companies holding exploration permit areas along the Athabasca River. A perusal of the values reported for bulk densities and porosities indicates that many of them are grossly erroneous. The object of the study herein presented was to devise a method for testing the accuracy of porosity data to the end of eliminating useless data from reported values. The remaining material could then be used for deducting the ranges of variations of bulk densities, porosities and saturations with oil and with water.

The writer has found it useful to divide the material making up the McMurray-oil-sand formation into three categories, namely: good grade oil sand containing 10% by weight of oil or more; shale containing 4% or less of oil; and interbedded oil sand and shale containing between 4% and 10% of oil. The present study is concerned only with good grade oil sand.

It so happened that the analyses of good grade oil sand available for study were from cores cut from sections of the McMurray formation that were predominantly shale and interbedded oil sand and shale. As a consequence, the mechanical analyses of the oil-sand aggregates show many examples of high silt content. In large masses of good grade oil sand, such as would be suitable for mining operations, silt contents will correspond to the lower, rather than the higher, values shown in the tables of analyses.

The direct method for determining the porosity and the percent saturation with oil and water is to measure the volume and the weight of a suitable sample of oil sand, and then to determine its composition in terms of water, oil and mineral matter. Oil sand is an unconsolidated material. It is held together by the content of viscous oil. Handling easily disturbs the natural packing. The analysis for composition should be made on the sample used for the bulk density determination or at least on material that is strictly comparable to this sample. It can be realized that unless real care is exercised, large errors can occur.

An indirect method of determining porosity is to use the sieve analysis of the mineral aggregate of the sample. This method cannot be regarded as accurate, but it can be made precise enough to test whether the directly determined porosity is reasonably accurate. A large number of direct analyses, from which wrong data have been rejected, provide a basis for calculating the range of variations of porosities and saturations.